1) Field of the Invention
The present invention relates to a process and a device for treating raw manure in order to produce a solid fertilizer, a liquid fertilizer, and water that possibly complies with environmental standards and can be safely returned to the environment or simply be recycled. In particular, the process and the device are adapted for the separation and the separate treatment of the liquid and solid components of pig manure, by utilizing natural stone and/or industrial derivative dust, as sedimentation agent for the colloidal particles of manure. In addition to upgrading manure, these process and device allow for an upgrading of residues from stone quarries.
2) Description of the Prior Art
The establishment of large hog farms causes increasing problems with respect to the management of pig manure. Conventionally, pig breeders get rid of pig manure by scattering it on agricultural lands. Although this solution is economical, it creates increasing problems, such as contamination of the air caused by bad odors, subterranean water and water sources contamination, as well as soil contamination due to the large quantities of waste. To overcome these problems, farmers rely more and more on transportation of manure by trucks in order to have far away lands at their disposal. This situation however leads to disadvantages, such as an increase in the cost associated with scattering and the difficulties resulting from transporting a liquid material.
Instead of wasting time in selecting a way to get rid of manure, investigators have concentrated on the modes of treating manure. Among those, bio-filtration by means of biological materials such as peat moss or straw should be mentioned. This method has the advantage that it does not cause secondary pollution, allows a reduction of the odors by 60% to 80% and is a technology that is not expensive and easy to install, because it can be used in restricted size areas. However, bio-filters should be replaced periodically and provide no upgrading of the organic matter. Another strategy aiming at adding additives to manure causes a reduction of the odors, from 70% to 85%, a reduction of the solid matter and a reduction of ammonia. The additives used may be masking agents, chemical agents capable of absorbing odors or also biological agents. In addition to being costly, the results obtained by using this strategy are to this day moderate.
The addition of additives to pig's feed constitutes an alternative to reduce odors and the quantities of ammonia in pig manure. As a matter of fact, agents such as amino acids, zeolites, coal, plant extracts, enzymes, microbes or salts may be added to the feed in order to improve food conversion and pig growth performances. This technology is however also costly and the efficiency of this method is not unanimous in commercial markets. Other breeders elect simply to cover their manure sump with covers of different nature, thereby preventing the emission of bad odors, while others elect to provide biological tree barriers around their installations, thus preventing bad odors from being spread around.
The prior art also describes processes that aim at separating the solid and liquid components that are present in pig manure. The U.S. Patent published under U.S. Pat. No. 4,193,206 describes a process for drying manure and filtering water. This process requires thermal drying or mechanical dehydration in a cylindrical chamber provided with porous walls. The U.S. Patent published under U.S. Pat. No. 4,270,279 describes a method for drying and sterilizing contaminated sludge by drying and fragmenting it into small pieces. The U.S. Patent published under U.S. Pat. No. 4,295,972, for its part, describes a method for treating water containing pollutants. This method comprises among others a step in which calcium oxide is added to contaminated water for a preliminary drying and the compound obtained is converted into granules. The U.S. Patent published under U.S. Pat. No. 5,013,458 describes a process and an apparatus allowing a reduction of pathogens and waste. This method includes a hydration step that is carried out by raising the pH of the waste sludge, allowing heat to be released. The U.S. Patent published under U.S. Pat. No. 5,885,461 describes a process and a system aiming at treating manures of domestic animals such as pigs, comprising the steps of compressing manure to separate liquids and solids, and drying the contaminated sludge. The addition of calcium carbonate causes a reduction of bad odors and the addition of polymers during the step of compressing sludge helps to separate the liquid that is present in the sludge. The liquid obtained is thereafter treated with a filtering membrane which makes it possible to remove undesirable elements from the liquid. The filtered liquid is possibly returned to the environment.
Although the latter process has interesting characteristics, the separation of the solid and liquid components that are present in manure requires an additional mechanical step that involves additional energy cost. Moreover, no method is provided for the addition of a precipitating agent to cause the separation of the solid and liquid components of manure in order to separately treat these two phases.
U.S. Pat. No. 6,409,788 recommends the use of a flocculating agent and chemical products that helps to precipitate phosphates, said flocculating agent and chemical products being associated with a base and an ammonia retention agent. We are therefore concerned with an expensive process that is limited to the separation of phosphates and the formation of a very impure liquid phase.
It would therefore be interesting to have at one's disposal a process permitting to treat raw manure and to upgrade quarry residues, which could be used as an agent for precipitating solid particles.